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 2.GQ Geiger Muller Counter
 High CPM

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T O P I C    R E V I E W
Virg Posted - 05/14/2021 : 10:57:59
Hi everyone,
I have a GMC 320+.Today I was outside, having an average CPM of 30 (inside the house it's 25).I was walking in the grass carrying the counter upside-down when suddenly I've got a reading of 1372 CPM. The sound was on, and the clic was very fast. The readings were higher with the counter upside-down, the wind was blowing and it was sunny. Not able to reproduce it inside. It does that only outside. The readings aren't higher at ground level. The readings are lower if the counter's screen is up. So I'm having readings from 400 to 1300 CPM. That's a max of 7.59 uSv/h.. Anyone has an explanation?? I'm not living near a nuclear station. Only a cyclotron for medical isotopes and research. Is the wind and/or direct sunlight can affect readings?
4   L A T E S T    R E P L I E S    (Newest First)
Breizh Posted - 06/08/2021 : 00:19:51
Hi Virginie,

You have to do a new reading on the same place for at least 20 minutes.Place your geiger counter in a plastic bag on the grass.Make an analysis with excell or better in libre office. Search the maximal value. Make a diagram. Good luck.

In the meantime have a look to my video:
EmfDev Posted - 05/14/2021 : 15:38:58
That is great!! Please email support your order number / address at and let them know you wanted the UV filter for your geiger counter tube.
Virg Posted - 05/14/2021 : 12:35:37
Thanks for the explanation! I would be interested to get that uv filter, how can I get it?
EmfDev Posted - 05/14/2021 : 12:05:36
Hi Virg, it is more likely that the tube counts is coming from UV light from the sun and not from radioactive source. This is a nature of glass geiger tubes. Currently we have a workaround solution by putting a tube UV filter to avoid UV light causing false counts. If you want we can send it to you so you can install it. Should be not hard but need to open the cover and reinstall the tube. Or you can contact support to install the UV filter.

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